According to the automake manual, CPPFLAGS (aka INCLUDES, as spelled
in automake 1.9.6) should only include -I, -D, and -U directives; more
generic directives like -Wall belong in CFLAGS since they affect more
phases of the build process. Therefore, we should be sticking CFLAGS
additions into a CFLAGS container, not a CPPFLAGS container.
* src/Makefile.am (INCLUDES): Move CFLAGS items...
(AM_CFLAGS): ...to their proper location.
* python/Makefile.am (INCLUDES, AM_CFLAGS): Likewise.
* tests/Makefile.am (INCLUDES, AM_CFLAGS): Likewise.
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